linux-kernel - Re: [PATCH v3 0/6] arm64: qcom: allow up to 4 lanes for the Type-C DisplayPort Altmode

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Message-ID: <9037fefe-aa40-4884-97ee-b81ff8346944@oss.qualcomm.com>
Date: Wed, 28 May 2025 13:13:26 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v3 0/6] arm64: qcom: allow up to 4 lanes for the Type-C
 DisplayPort Altmode

On 5/28/25 11:00 AM, Dmitry Baryshkov wrote:
> On Wed, May 28, 2025 at 12:24:02AM +0200, Konrad Dybcio wrote:
>> On 5/27/25 11:10 PM, Dmitry Baryshkov wrote:
>>> On Tue, May 27, 2025 at 10:40:02PM +0200, Konrad Dybcio wrote:
>>>> Register a typec mux in order to change the PHY mode on the Type-C
>>>> mux events depending on the mode and the svid when in Altmode setup.
>>>>
>>>> The DisplayPort phy should be left enabled if is still powered on
>>>> by the DRM DisplayPort controller, so bail out until the DisplayPort
>>>> PHY is not powered off.
>>>
>>> This series doesn't seem to solve the USB side of a problem. When the
>>> PHY is being switch to the 4-lane mode, USB controller looses PIPE
>>> clock, so it needs to be switched to the USB-2 mode.
>>
>> I didn't find issues with that on X13s.. Not sure if it's related, but
>> on the SL7, after plugging in a 4ln DP connection, I need to plug in
>> the USB thumb drive twice for the first time (only in that sequence)
> 
> Might be.
> 
>> But there's nothing interesting in dmesg and the phy seems to be
>> programmed with the same values on both the initial and the subsequent
>> working plug-in
> 
> Please try using a DP dongle with USB 2 passthrough (there are some).
> Or just emulate this by enabling DP PHY / DP chain for plugged in USB3
> devices. Would you be able to see the USB device on a bus?

I only have a dongle with both display and usb that does 2ln dp
(I tested 4ln dp on a type-c display that I don't think has a hub)

USB3 - yes, USB2 - no (but it works after a replug)

Are you talking about essentially doing qcom,select-utmi-as-pipe-clk
at runtime?

Konrad